The present invention concerns a lap winding apparatus for producing a in which a batt is wound onto a core which is rotatable about a fixed axle.
In a lap winding apparatus is known from GB 329 871 in which an endless belt is driven over two deflecting rolls and the core to form a loop that is tensioned by a tensioning arrangement. The belt, at the beginning of the lap winding process, contacts a small portion of the core circumference. The wrapping angle is less than 600. Tensioning of the belt is effected by means of an angled lever at one arm of which a deflecting roll embraced by the belt is provided and at the other arm of which a weight is provided which for setting the tensioning force can be adjusted manually.
In this known lap winding apparatus, a kind of pulling effect can occur due to the local strain affecting the baft, which causes the lap layers to be shifted against each other. Due to the friction, felting of the baft can occur, which causes problems, impairing product quality, as the lap unrolls.
It thus is the goal of the present invention to create a lap winding apparatus of the above mentioned type which is simple in lay-out and which permits production of high quality taps which can be unrolled without problem.
This goal according to the invention is achieved in that the core is rotatable about a fixed axis and the two deflecting rolls are dimensioned and positioned in such a manner that the belt loop at the beginning of the lap winding process embraces the core over an initial minimum wrapping angle of 120xc2x0 or larger and preferably of 180xc2x0 or larger and that the tensioning device for generating a tensioning force depending on the lap diameter is associated with a control device.
Since the rotatable core is, at the beginning of the lap winding process being surrounded over a large area by the belt, i.e. over a larger wrapping angle, the lap being formed from the beginning is put under a much more even pressure. Furthermore any possible formation of an oval shape of the lap can be effectively counteracted by correspondingly adapting the tensioning force to the current lap diameter. The fixed axis of the core notwithstanding, occurrence of a pulling effect can be virtually excluded. In this arrangement, shifting of the batt layers against each other and felting of the batt is prevented. Thus, a high quality lap is produced which can be unrolled without problems in subsequent processing of the baft.
Particularly in view of negligible formation of blisters and of further improved unrolling properties, it proves advantageous if the tensioning device is controlled by the control device in such a manner that the tensioning force diminishes as the lap diameter increases until a pre-determinable lap size is reached. In this process the tensioning force preferentially diminishes linearly as the lap diameter increases until a pre-determinable lap size is reached. Owing to the harder pressure applied in lap winding during the beginning stages, plasticity of the of the lap is reduced and the lap gains more stability in itself which positively influences the unrolling properties as well as the quality.
A further advantage is gained if the pre-determinable lap size is chosen smaller than the final lap size and if the tensioning force is maintained constant until the pre-determinable lap size is reached. In this process, it is provided preferentially that while the lap diameter increases, the tensioning force is reduced over the major part of the lap winding process and that only towards the end of the lap winding process is maintained constant at a value above zero until the final lap size is reached.
The control device, which preferentially is an electronic control device, can be associated with a sensor which scans the lap diameter directly. In principle it also is possible to provide a measuring device which monitors the baft length fed to the lap winding apparatus in order to obtain a signal representative of the lap diameter for the control device.
In a preferred embodiment of the present invention, the tensioning device comprises a tensioning roll associated with a linear guide arrangement. In this arrangement, the belt is tensioned in a plane parallel to the plane containing the axes of the two deflecting rolls between which the belt loop forms. Particularly, if control of the tensioning force is to be effected as precisely as possible,. it also proves advantageous if the belt embraces the tensioning roll, independently of the position of the latter, always over a wrapping angle of 180xc2x0. In this case, the two belt sections facing each other extend mutually parallel in the area of the tensioning roll, which permits, among other advantages, more precision in the control of the tensioning force. Adjustment of the position of the tensioning roll can be effected using an electric, hydraulic or pneumatic drive associated with the control device, the drive appropriately comprising a cylinder/piston unit.
The belt expediently is driven via at least one of the deflecting rolls. For controlling the belt drive speed in an open loop or closed loop control system, the belt drive can be associated with the control device. The belt drive speed can be varied in function of the lap diameter and can e.g. decrease as the lap diameter increases. The open or closed loop control system can be laid out in such a manner that the belt drive speed at the beginning of any lap winding process is increased from zero to a predetermined value. The belt drive can be frequency controlled using an invertor or similar devices. It also can be imagined that the belt drive speed be maintained constant at least temporarily.
If the core is formed by a tube, this tube can be placed e.g. on an extension each on the two lap disks facing each other between which the tube preferentially is clamped.
The two deflecting rolls, between which the belt loop forms, for ejecting the lap can be preferentially moved apart relative to each other while simultaneously the belt is tensioned.
According to a particularly advantageous embodiment of the invention removal of at least one of the lap discs, effected e.g. by extending, traversing or similar movements, ejection of the lap, transfer of the lap to a transporting device or similar steps and/or inserting and clamping of a new empty tube is automated at least partially and again is controlled by means of the control device.
In order to avoid electrostatic charges, the belt is made of a Kevlar material.
The lap winding apparatus is applicable in particular in combing where a baft or web e.g. delivered by a drafting system via deflecting plates, via calendar rolls and/or via similar elements is taken up. The completed lap subsequently is fed to a combing machine.